Electrical connectors are commonly used in the electronics industry in order to facilitate the interconnecton of various components. Such connectors are typically formed as a row of a specified number of positions, with each position containing one or more connection sites. For example, a twelve position dual in-line connector will have twelve positions of two pins each, for a total of 24 pins or connection sites.
Electrical connectors may generally be divided into two classes: through-hole connectors and surface mount connectors. When a through-hole connector is mounted onto a printed circuit board, each of the connector pins extends through a respective through-hole in the printed circuit board. In contrast, a surface mount connector is contained entirely on one side of the circuit board. The present invention relates primarily to through-hole connectors.
Through-hole connectors include conductive pins which protrude from their bottom surfaces and extend through holes formed in a printed circuit board when the connector is mounted thereon. Each of the pins must be soldered to a conductive trace on either the same or opposite sides of the printed circuit board from the connector body. For example, if a through-hole connector has 24 pins, 24 holes will be formed in the printed circuit board with the same dimensional spacing and size as the connector pins.
One of the problems commonly associated with through-hole connectors involves the soldering of the connector to the circuit board. There are currently 3 different techniques used in the connector industry to solder a connector to a board: 1) wave soldering; 2) solder preforms; and 3) hand soldering. Each of these techniques suffer from the following described drawbacks, which are significant as known to those of ordinary skill in the art.
Wave soldering involves the submersion of the tail of the connector pin (that portion of the pin extending through the through-hole) and the mounting surface (the surface to which the tail is soldered) in an actual wave of hot, liquid solder. The liquid solder is contain in a bath or tub, and the wave is created by ultrasonic means as known in the art. The solder coats the tail and the mounting surface, causing the pin to be fastened to the mounting surface when the solder hardens.
One problem associated with wave soldering is that the solder covers all the parts in which it contacts. This results in the waste of solder material and increases the cost of soldering through-hole connectors. A second problem is that solder covers the tails that extend through the through-holes. This is particularly troublesome in applications in which long tails are extended through the through-holes in order to engage a second printed circuit board. The solder that clings to the long tails increases the cross-sectional area of that portion of the pin. This condition causes the pin to not fit through the holes of the second board. Thus, the solder must be removed from the tails, which is an expensive and time-consuming process.
Solder preforms are one attempt to address the problems associated with wave soldering. Solder preforms are essentially rings of solder paste that are press-fit onto the connector pin. The pin is then inserted into the through-hole until the preform is in contact with the connector body and the circuit board. The assembly is placed in an infrared oven to reflow the solder paste and solder the connector to the circuit board.
One of the problems associated with solder preforms is the cost of the preform. It is very expensive to preform the solder paste in a manner that allows it to be press-fit on a connector pin. A second problem is that solder preforms are not reliable. They tend to fall off the pin before it is inserted into the through-hole. A poor solder connection may result when this problem is not detected. Given the high quality standards required in the connector industry, this is an unacceptable result.
A final method of soldering pin connectors to circuit boards is to use hand soldering techniques. Hand soldering, while reliable, is expensive. It is also impracticable, if not impossible, to solder connectors including multiple rows of pins to a circuit board. For example, a connector with four rows of pins is common in the connector industry. It is impossible for a reliable solder connection to be obtained in the interior rows due to the limited amount of space between rows, which may be less than one millimeter for some types of connectors.
What is therefore needed is a technique for soldering through-hole connectors that addresses the foregoing shortcomings in the prior art. The technique should be clean, inexpensive and minimize the use of solder material. It should be reliable, yet adaptable for use in many different types of pin connector designs. Finally, the technique should be readily integratable into existing soldering methods and apparatus. The present invention is directed toward meeting each of these needs.